This invention relates to elongated tubular devices which are immersed into molten liquid metal. It relates specifically to the construction of consumable lance devices used to introduce oxygen or other gases into molten steel.
In metallurgical operations using continuous casting machines it has become necessary to tap the heats "hot" from the furnaces to insure sufficient temperature at delivery to the caster. Missed caster sequences require either (a) diverting pours into ingots, with the consequence of lower quality steel and higher production costs, (b) providing a ladle reheat furnace for raising the temperature of the liquid steel in the ladle or (c) blowing oxygen into the liquid steel through an oxygen lance to raise the temperature of the liquid steel to the required casting temperature. Heretofore, it has been the practice to use either water-cooled nonconsumable lances or refractory covered consumable lances during such oxygen blowing reheating operations.
Consumable lances in the past have used several designs. The first design injects oxygen into the molten steel bath through a centrally located longitudinal tubular steel member encased within a protective refractory covering.
Another design, as taught in U.S. Pat. No. 3,645,520, injects oxygen into the molten steel bath through a plurality of spirally wound tubular copper members encased within a protective refractory covering. Such spirally wound passageways have been developed to reduce or eliminate splash as the oxygen is injected into high carbon liquid steel.
As oxygen is injected into the liquid steel bath, the combination of high temperatures, and the rapid flow of oxygen through and around the tubular passageways and supporting structures of the aforementioned consumable lances, causes lance tip erosion at a rate of up to 12 inches/min. Such high erosion rates make it necessary to manufacture reheating lances with excessively long consumable tip portions. For example, in reheating a ladle, it may be necessary to increase the temperature of the liquid steel up to 50.degree. F. With a reheat rate of 5.degree. F. to 10.degree. F. per minute, and a lance wear rate of up to 12 inches/min., it is possible to consume 10 feet of reheating lance during a single reheating operation.